An optical scanning device that performs optical scanning by oscillating a reflector at a high speed, by using the resonance of a vibration system instead of by using a rotating reflector, such as a polygon mirror that is provided for an optical scanner, has been proposed in patent literature 1 and in patent literature 2. An oscillating member or an electrometer using the same operating principle is also proposed in patent literature 3.
An optical scanning element, which serves as an oscillation element included in such an optical scanning device, or in an electrometer, generally includes: a plate-shaped oscillating member; a torsion bar to which the oscillating member is fixed; and drive means for oscillating the oscillating member about the longitudinal axis of the torsion bar. Further, the drive means includes a magnet, which is attached with the oscillating member, and a coil for passing an alternating current, located opposite the magnet, and when the alternating current is supplied to the coil, the oscillating member is oscillated with an elastic deformation of the torsion bar. Therefore, a resonance phenomenon, due to the elastic deformation of the torsion bar, can be employed to oscillate the oscillating member, with a large deflection angle, using only a comparatively small amount of electric power.
It should be noted that the “deflection angle” represents an angle formed by two oscillation ends, at which the oscillation direction of the oscillating member is changed in a case wherein the oscillating member is oscillated about the longitudinal axis of the torsion bar.